[mrv]

I assume that the UK Prius has an
installed glass breakage sensor as
part of the alarm package?

In the US, the glass breakage sensor
is a separate accessory item, usually
installed by the dealer. It's
basically a microphone that is tuned
to the inside of the car, listening
for loud things like the sound of
breaking glass... A few people
reported having issues with the
sensitivity of the microphone set
too strong, so the alarm went off
during thunderstorms and other such
loud noises. There's just a simple
switch to turn down the microphone
a bit, which should fix the issue.

 

[mrv]

Re: Sensitive Anti-Theft protection

Thanks mrv but my alarum goes off when it rains with no sound of any loud noises. I tried knocking on the roof and the windscreen with the alarum set but I couldn't trigger it. It appears to be only heavy rain that does it. Can the sensitivity control be accessed easily??

I don't know.

I occasionally browse the prius_uk yahoogroup, and I've seen a few others with your problem there. I don't recall if there was a fix or anything posted, but you may want to look or ask there:
http://autos.groups.yahoo.com/group/prius_uk/